Heat dissipation in a computer system that typically includes a central processing unit ("CPU") is always a significant concern. This is due to the fact that heat is typically generated in the computer system during operation. If the heat generated inside the computer system is not properly dissipated, the temperature inside the computer system typically rises. The temperature rise in the computer system may cause the computer system to malfunction. One reason for the malfunction is that the electronic characteristics of many integrated circuit ("IC") devices vary depending on temperature. Another reason for the malfunction is that the heat generated by the computer system can cause the temperature inside the computer system to vary from point to point. This is typically the case when high density IC devices are employed that yield more heat than other IC devices in the system. The temperature variation from point to point inside the computer system may also cause the computer system to malfunction in addition, the IC devices may be damaged by the temperature rise.
One prior art scheme to dissipate heat from a computer system or a data processing system is to employ a forced-air cooling system in the computer system. Forced-air cooling typically accelerates the heat exchange from the IC devices of the computer system to air. This is typically accomplished by using a fan to force cold air flow through the IC devices. The heated air is then expelled from the computer system.
Another prior art scheme to improve the forced-air cooling system is to use metal cold plates that are connected to the IC devices of the computer system to remove the heat from the IC devices. The cold plates have a low thermal resistance and can more efficiently transfer the heat away from the IC devices. The cold plates are then cooled by the fan to blow cold air through them.
Power consumption in a computer system is also a significant concern. This is especially the case when the powered system is a portable unit. Therefore, when full operation of the computer system is not desired or necessary, it is important to control the power consumption of the computer system. One prior art scheme of conserving power in a computer system is to have a "sleeping mode" for the CPU of the computer system. This prior art scheme is described in U.S. Pat. No. 4,381,552, issued Apr. 26, 1983, and entitled STANDBY MODE CONTROLLER UTILIZING MICROPROCESSOR. The apparatus disclosed in the above-referenced patent generates a WAIT signal to the CPU when full operation is not required to put the CPU in a standby mode where power consumption is reduced. During this period, sampling occurs at intervals in order to activate the device fully when full operation is required.
When the CPU is put into the standby mode or "sleeping mode", the CPU may no longer need cooling because the CPU does not generate much heat when in standby mode. Therefore, the fan of the cooling system can be powered off at this time in order to further conserve the power of the computer system.
One prior scheme of controlling the fan uses temperature sensing devices. While this may be an effective way for controlling the speed of the fan to compensate for ambient temperature differences, one disadvantage of this prior scheme is that it does not work well for determining when the CPU no longer needs cooling due to a low effective (or stopped) clock rate. Another disadvantage of this prior approach is that the temperature sensing device must be placed in close proximity to the CPU in order to properly determine if the temperature of the CPU is rising. This typically increases technical difficulty in implementation because placing the temperature sense devices close to the CPU in the computer system is typically difficult. In addition, the implementation may be costly.
Another prior technique for controlling the power consumption of the fan is to have an output port (e.g., a register) written by software to directly control the on and off condition of the fan. One disadvantage of this prior technique is that because the power control of the fan is accomplished by software, there is always the possibility of a software bug or error. The software bug or error may cause the fan to be left off when the CPU is actually running. This could lead to heat damage of the CPU.